Not a little task, correcting tags and routes of farm to market roads. It is essential if routing is to work correctly in rural areas. Wikipedia states that there are fifty thousand miles of FM designated roads in Texas. Congratulations on the completion of big task.

Are all FM roads built to the same standards? Are road widths, surface, shoulders and the number of lanes uniform across the state? If that were so then correcting the tags would be easier but I suspect that they vary widely.

In Missouri, where I have been correcting rural state roads, there is no standard. There is a system of state roads each designated with a letter code. The codes are reused in each county as needed. Adjacent counties may have roads with the same 'State Highway B' designation. In a few cases there may be two separate state roads with the same letter in a single county.

The state does not have a system of categorizing rural roads other than the Supplemental State Highway designation. Some work was done in the western counties around Kansas City to classify the roads functionally as arterial or collector but was stopped in 2008 due to budget cuts. As a result the classification of roads in Missouri is left up to each individual mapper. Road may be tagged as tertiary or secondary in rural areas. Currently most road are untouched, left incorrectly tagged as residential from the TIGER import.

When looking at the condition of tags in unedited roads in this area it makes your accomplishment in Texas so much more impressive.